Servo valve flapper and nozzle structure

ABSTRACT

An integral flapper and nozzle structure for a servo valve assembly whereby the flapper, orifices and nozzles are formed by sheets of metal formed into a single component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 17/543,923filed Dec. 7, 2021 which claims priority to European Patent ApplicationNo. 20461601.5 filed Dec. 22, 2020, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to servo valves used to transferquantities of, or manage the flow of fluids, e.g., oil, fuel, or air,and, in particular, to a flapper and nozzle structure for a servo valve.

BACKGROUND

Servo valves find a wide range of applications for controlling air,fuel, oil or other fluid flows to effect driving or control of anotherpart, e.g., an actuator or in fuel control systems.

A servo valve assembly may include a drive assembly such as a motorcontrolled by a control current which controls fluid flow to or from anactuator. Generally, a servo valve transforms an input control signalinto movement of an actuator cylinder. The actuator controls anothercomponent which, in some examples, may be a valve. In other words, aservo valve acts as a controller, which commands the actuator, whichchanges the position of a valve's flow modulating feature.

Such mechanisms are used, for example, in various parts of aircraftwhere the management of fluid/air flow is required, such as in enginefuel control, oil flow, engine bleeding systems, anti-ice systems, airconditioning systems and cabin pressure systems. Servo valves also arewidely used to control the flow and pressure of pneumatic and hydraulicfluids to an actuator, e.g. to control moving parts such as flightcontrol surfaces, flaps, landing gear, and in applications whereaccurate position or flow rate control is required. Some examples ofapplications are aircraft, automotive systems and in the space industry.

Conventionally, servo valve systems operate by obtaining pressurisedfluid from a high pressure source which is transmitted through a loadfrom which the fluid is output as a control fluid. Various types ofservo valves are known, examples of which are described in UK PatentApplication No. GB 2104249A, U.S. Patent Application Publication No.2015/0047729 and U.S. Pat. No. 9,309,900.

Electrohydraulic servo valves can have a first stage with a motor, e.g.an electrical or electromagnetic force motor or torque motor,controlling flow of a hydraulic fluid to drive a valve member e.g. aspool valve of a second stage, which, in turn, can control flow ofhydraulic fluid to an actuator for driving a load. The motor can operateto position a moveable member, such as a flapper, in response to aninput drive signal or control current, to drive the second stage valvemember e.g. a spool valve by controlling the flow of fluid acting on thespool. Movement of the spool causes alignment between the ports andfluid channels to be changed to define different flow paths for thecontrol flow. Such systems are known in the art and will not bedescribed here in detail.

Such conventional systems will be described in more detail below withreference to FIG. 1 .

Conventional flapper-type systems are fairly large, bulky systems with acomplex construction of several moving parts and channels, which meansthat there are several potential points of failure. The individual partsand orifices all need to be very precisely manufactured and thenassembled into a valve assembly and calibrated to ensure proper andprecise operation of the servo valve. The flapper is usually part of atorque motor, which is a separate sub-assembly and so this needs to beproperly calibrated to the spool sub-assembly. Any slight imperfectionin the geometry of any of the parts can result in faulty operation ofthe assembly. Such precise manufacturing and calibration is complex andtime consuming. In addition, it is essential that no leakage occurs inthe fluid circuit and so proper sealing needs to be ensured by use ofseals, O-rings, brazing or the like.

There is a need for improved flapper-type servo valve arrangements thatcan handle large fluid flows effectively and at high operationfrequency, but with fewer expensive and complex parts and which aresimple to manufacture and assemble, whilst retaining a compact andreliable, responsive design and with the required precision.

SUMMARY

The present disclosure provides an integral flapper and nozzle structurefor a servo valve whereby the flapper, orifices and nozzles are formedby sheets of metal formed into a single component.

The flapper is preferably formed in a first sheet of metal, the sheetbeing formed of a compliant metal, and the orifices are formed in asecond sheet of metal, the first and second sheets being co-located suchthat the orifices are in a fixed spatial position relative to theflapper.

The structure may comprise a first sheet of flexible metal cut to definetwo opposing, flexible arm portions and provided, between the armportions, with first and second opposing nozzles, first and second fixedorifices, a first channel between the first nozzle and the first orificeand a second channel between the second nozzle and the second orifice.

A first cover plate may be secured to a first face of the first sheetand a second cover plate may be secured to a second, opposite, face ofthe first sheet, one of the first and second cover plates provided withfirst and second output ports and a single supply port common to thefirst and second nozzles.

A slot may be provided through the structure to receive a drive memberfrom a drive motor to move the flapper.

Also provided is a servo valve assembly comprising a spool body, a drivemotor, a drive member extending from the drive motor to control movementof the spool body, and an integral flapper and nozzle structure asclaimed in any preceding claim, whereby the integral flapper and nozzlestructure is positioned such that movement of the drive member causesmovement of the flapper relative to the nozzles to regulate fluid flowto the spool body to cause movement of the spool body.

Also provided is method of forming an integral flapper and nozzlestructure as described above, the method comprising forming, by cutting,the flapper, nozzles and orifices in the sheets of metal such that theflapper is moveable relative to the nozzles.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments will now be described, by way of example only,with reference to the drawings.

FIG. 1 is a sectional view of a conventional flapper type servo valveassembly;

FIG. 2 is a simple schematic view to explain operation of a conventionalflapper type servo valve assembly.

FIGS. 3A and 3B show two sides of a flapper structure for a servo valveaccording to the disclosure.

FIGS. 4A to 4C shows steps of manufacturing a structure according to thedisclosure.

FIG. 5 is a perspective view of a section of the structure after thesteps shown in FIGS. 4A to 4C.

FIG. 6A is a section of the structure of FIG. 5 into which a slot iscut.

FIGS. 6B and 6C illustrate how the flapper is formed in the structure.

FIGS. 7A and 7B illustrate operation of the structure of the disclosure.

FIG. 8 is a perspective view illustrating assembly of the structure intoa servo valve assembly.

FIG. 9 is a top view of the servo valve assembly of FIG. 8 with theflapper structure inserted therein.

FIG. 10 is a detail section view of a servo valve assembly having aflapper structure according to the disclosure.

FIG. 11 is an alternative sectional view of the assembly of FIG. 10 .

DETAILED DESCRIPTION

Servo valves are generally used when accurate position control isrequired, such as, for example, control of a primary flight surface.Servo valves can be used to control pneumatic or hydraulic actuators ormotors. They are common in industries which include, but are not limitedto, automotive systems, aircraft and the space industry.

A known type of servo valve has a flapper and nozzle arrangement.

FIG. 1 shows generally a known arrangement of a flapper and nozzle servovalve. The assembly comprises a torque motor subsystem 300 and aflapper-nozzle subsystem 400. In more detail, the assembly comprises aflapper 6 disposed in a flapper cavity 7, a pair of nozzles 9 disposedin a nozzle housing, and an electromagnet 8 surrounding an armature 5.The armature has opposed tips, which protrude through gaps in a housingsurrounding the electromagnet, and which are arranged to leave spacesbetween the armature and the housing.

The electromagnet is connected to an electrical input (not shown) andthe armature 5 is connected in a perpendicular manner to the flapper 6,or is an integral part of the flapper—the integral part beingperpendicular to the flapper. The electromagnet includes coils thatsurround the armature and a set of permanent magnets that surround thecoils. When a current is applied to the coils from the electrical input,magnetic flux acting on the ends of the armature is developed. Thedirection of the magnetic flux (force) depends on the sign (direction)of the current. The magnetic flux will cause the armature tips to beattracted to the electromagnet (current direction determines whichmagnetic pole is attracting and which one is repelling) thus varying thesize of the spaces. This magnetic force creates an applied torque on theflapper, which is proportional to the applied current. The flapperrotates and interacts with the nozzles.

Nozzles 9 are housed within a respective nozzle cavity in the housing,and comprise a fluid outlet and fluid inlet. The housing also has aport, which allows communication of fluid to the nozzles. The flappercomprises a blocking element at an end thereof which interacts withfluid outlets of nozzles to provide metering of fluid from the fluidoutlets to a fluid port in the housing. The fluid port in turn allowscommunication of fluid pressure downstream to a spool valve and actuatorarrangement (not shown). The positioning of the flapper between nozzles(controlled by the movement of the armature via electromagnet) willcontrol the amount of fluid pressure communicated to the spool valve andactuator arrangement (not shown), which can be used to control actuatormovement.

The flows of pressurised fluid in a conventional flapper type system canalso be explained with reference to the simple schematic of FIG. 2 . Thehydraulic fluid to be regulated by the spool valve for moving theactuator is delivered from a fluid supply with a constant pressure Psvia orifices 10,20. At the orifices, the fluid is divided into twostreams. One stream 6,7 is provided to the ends of the valve spool. Theother stream is directed to the flapper nozzles 9′, 9″ where it is usedto control movement of the spool due to the position of the flapper 6.Depending on the gap between the flapper and the respective nozzles 9′,9″ more or less flow will be possible through each nozzle causingpressure differences in control channels P1 and P2 which results inpressures differences at the ends of the spool causing movement of thespool. Thus, if the flapper 6 is closer to nozzle 9′ than nozzle 9″,then more flow is possible through nozzle 9″ and less through nozzle 9′.If less flow is possible through nozzle 9′, more fluid flows to the endof the spool through channel 70 than through channel 60 thus increasingthe pressure at end A of the spool compared to end B and thus causingthe spool to move in direction X. Conversely, if the flapper is closerto nozzle 9″, pressure increases at end B causing the spool to move indirection Y.

Although the flapper and nozzle type of servo valve arrangement shown inFIG. 1 can be effective at controlling an actuator, it has been foundthat limitations nevertheless exist. For example: in order to providethe correct limitations on flapper and armature movement, the spacesmust be manufactured, assembled and calibrated very precisely to verytight tolerances, as must the spacing of the nozzles from the flapper.Moreover, there is also a general desire to reduce servo valve weightand simplify its manufacture, construction and operation, as well asimprove the operational pressures and frequencies that may be realisedwith such servo valve arrangements.

The assembly of the present disclosure is an integral flapper and nozzlestructure for a servo valve whereby the flapper, orifices and nozzlesare formed by sheets of metal formed into a single component.

FIGS. 3A and 3B show, respectively, the two sides of the integralstructure. The features of the flapper 15, nozzles 13,14 and orifices11,12 are formed in a generally rectangular sheet metal structure. Theorifices 11, 12 are formed in a first sheet and are designed to be fixedin position relative to the other sheet into which the flapper 15 isformed. The flapper 15 is formed in a sheet of compliant material suchthat its position or spacing relative to the nozzles 13,14 can bevaried.

The manufacturing steps are explained with reference to FIGS. 4A to 4C.

First, as shown in FIG. 4A a sheet 50 of flexible material of generallyrectangular shape is cut to define two opposing arm portions 51, 52. Thearms are elastic such that they can move within the plate structure aswill be described further below.

In the area of the sheet 60 defined between the cuts 53, 53 that definethe arm portions 51,52, shapes are cut to define two opposing nozzles61,62 (13, 14 in FIG. 3B) and two constant orifices 63, 64 (11, 12 inFIG. 3B) and supply channels 65,66 between the orifices and the nozzles.The cutting has to be performed in a highly precise manner e.g. by lasercutting, water-jet cutting, wire-EDM cutting or photo-etching.

Once this structure has been cut into the metal sheet 50 a cover plate70,80 is fixed to either side of the sheet 50. One of the cover plates80 is provided with two output ports 81,82 for piloting channels for thevalve spool (not shown) and a single supply port 83 common to the twonozzles 61,62. This creates a sandwich structure shown in section inFIG. 5 . The cover plates 70,80 can be fixed to the metal sheet 50 byany method that ensures strength and tightness of fixation e.g. byelectron beam welding.

A slot 90 is then formed through the sandwich layers as shown in FIG. 6. This allows a drive member (not shown here) from a torque motor toengage with the flapper for moving the flapper in response to the servovalve control command. It is also possible to locate a feedback spring(not shown) in this slot to provide feedback from the valve spool to theflapper.

The next stage involves cutting through the sandwich structure, as shownin FIGS. 6B and 6C, along a cutting line 100 to define the flapper 110.The cut defining the flapper 110 is made such as to define a preciselycalibrated gap 120 between the flapper 110 and the nozzles 61.62. It iscritical that the position of the nozzles 61,62 with respect to theflapper 110 is precisely set at this stage. The gaps 120 between theflapper and the nozzles may be the same or different for each nozzle butmust be precisely set.

This process results in an integral flapper and nozzle and orificestructure in the form of a single sandwich package as shown in e.g.FIGS. 3A and 3B.

Operation of the flapper and nozzle structure can be described withrespect to FIGS. 7A and 7B.

In response to a command, e.g. sent to a torque motor or other driveassembly, a drive member (not shown) is moved. The drive member isengaged with the flapper 110 e.g. by extending through the slot 90. Thiscauses the flapper 110 to move (shown by the arrow) with respect to therest of the structure containing the nozzles. This movement is enabledby the elasticity of the arms 51,52. The elasticity also biases theflapper 110 to return to the original position when the force of thedrive member is removed.

As can be seen, as the flapper 110 moves, the gaps between the flapperand the respective nozzles 61,62 change. In the example shown, as theflapper 110 moves in the direction of the arrow, the gap 120 between theflapper and the nozzle 61 (13 in FIG. 3B) increases, while the gap 120′between the flapper and the other nozzle 61 decreases.

When assembled into a servo valve assembly, the flapper 110 operates tovary flow between the respective nozzles resulting in a pressuredifferential that causes movement of the valve spool as previouslydescribed for conventional systems.

FIGS. 8 and 9 show how the flapper and nozzle structure 200 can beassembled into the body of a servo-valve assembly between the motor (notshown) and the valve body 300. A gasket 130 may be positioned as a sealbetween the flapper structure and the valve body.

FIGS. 10 and 11 show the flapper and nozzle structure 200 fitted into aservo valve assembly to cause movement of the valve spool 400. The drivemember 500 can be seen extending from the drive sub-assembly where themotor would be located. This extends through the slot 90 in the flapperand nozzle structure 200 and is drive in response to a control commandto move the flapper 110 as described above with reference to FIGS. 7Aand 7B. A spring or feedback wire 700 may also extend through the slotto provide feedback from the valve spool 400.

Movement of the flapper with respect to the nozzles, as described above,varies the gap between the flapper and the nozzles and, hence, the fluidflow through the nozzles, which, in turn gives rise to a pressuredifferential in the channels feeding the respective ends of the spool400, this causing axial movement of the spool.

Compared to known flapper and nozzle designs whereby the various partsare formed separately and then assembled and calibrated, the singlepackage structure of this disclosure, integrating the nozzles andorifices and flapper, means that the critical components of the servovalve control structure can all be made precisely and with repeatableaccuracy as a single structure. This can then be easily replaced in thevalve even during service.

In addition, no additional assembly and sealing is required to mount theflapper relative to the nozzles and relative to the orifices and soadditional sealing to prevent leakage is not required.

The structure is simple and cost effective to manufacture and assembleinto the valve body. The structure can also be easily designed fordifferent performance requirements merely by making different size cutsduring manufacture.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. The structureof claim 1, further comprising a slot formed through the sheets of metalarranged to receive a drive member from a drive motor to move theflapper.
 6. (canceled)
 7. A method of forming an integral flapper andnozzle structure, the method comprising: forming, by cutting, theflapper, nozzles and orifices in sheets of metal such that the flapperis moveable relative to the nozzles; wherein the flapper is formed in afirst sheet of metal, the first sheet is formed of a compliant metal;wherein the orifices are formed in a second sheet of flexible metal,co-locating the first and second sheets of metal such that the orificesare in a fixed spatial position relative to the flapper; wherein formingalso includes cutting the second sheet of flexible metal to define twoopposing, flexible arm portions and provided, between the arm portions,with first and second opposing nozzles, first and second fixed orifices,a first channel between the first nozzle and the first orifice and asecond channel between the second nozzle and the second orifice. 8.(canceled)
 9. The method of claim 7, wherein the cutting is by lasercutting, water-jet cutting, wire-EDM cutting or photoetching.
 10. Themethod of claim 7, further comprising: fixing first and second coverplates to, respectively, first and second faces of the first compliantmetal sheet; and forming, in one of the cover plates, two output portsand a single supply port common to the first and second nozzles.
 11. Themethod of claim 7, further comprising forming a slot through thestructure to receive a drive member of a drive motor to cause movementof the flapper.
 12. The method of claim 7, wherein the flapper is formedby cutting through the structure to form a gap between the flapper andthe nozzles.
 13. The method of claim 7, wherein the sheets of metaldefine a rectangular sheet metal structure such that the flapper formedin the first sheet is arranged over the second sheet so that the flapperis moveable between the arm portions of the second sheet to allow theflapper move relative to first and second opposing nozzles.